Vapor electric discharge device



Oct. 6, 1936. 'r. w. FRECH VAPOR ELECTRIC DISCHARGE DEVICE Filed Aug.18, 1934 lnvhtov: Theodore W. Frech, b w 88W 9 fi/flfi i5 Attorney.

Patented Oct. 6, 1936 UNITED STATES PATENT OFFICE Theodore W. Frech,Shaker Heights, Ohio, assignor to General Electric Company, acorporation of New York Application August 18, 1934, Serial No. 740,508

10 Claim.

This invention relates to gaseous or vapor electric discharge devices ofa general type exemplifled by metal vapor lamps, and particularly todevices containing a substance (like sodium, potassium, or other alkalimetal) which while gaseous or vaporous during operation of the device isreadily condensible,in part, at least,and which may tend to attack somepart of the device at temperatures attained during its operation.Examples of susceptible lamp parts are lead wire seals, a glass stem, oran area of glass envelope wall which is unresistant, as where aprotective glaze on the inner surface has been destroyed by local fusionof the envelope in lamp manufacture. In such cases as these, it isdesirable to exclude the hot substance from the susceptible parts, orfrom the internal region of the device where they are located. Othercases may also aoccur where it is desirable to exclude alkali metalvapor or other vaporous working substance or material more or lesscompletely from certain regions of the device, irrespective of possibleattack of metal vapor on any part. My invention is less expensive thanmeans hitherto employed for similar purposes in metal vapor lamps, andallows the lamp to be made shorter than usual heretofore. It isespecially adaptable and advantageous for tubular lamps, where anordinary bulb neck is usually not desired.

In accordance with my invention, I arrange that the portion or region ofthe device (or of its envelope) from which for any reason it is desiredto exclude the hot substance shall be kept cool enough to condense thesubstance, or even to solidify it. I may specially construct the devicewith one or more recesses opening oil from its main internal space, toinclude the susceptible part or area, and to be cooled sumciently belowthe general temperature of the device to assure condensation, etc.Ordinarily, the usual exter-- nal cooling of the envelope wallsurrounding a suitable recess will suflice, without any special coolingprovisions,even when the device is enclosed in a heat-conserving vacuumjacket, as is customary with sodium vapor lamps. (As sodium, forexample, boils at about 877 C., as against temperature around 220-275 C.for the envelope walls of a sodium lamp, only a relative coolness of,the recess is required, because the sodium is'continually condensing allover the inner envelope surface and vaporizing again, with a tendency toaccumulate and remain in any region that is especially cool, owing tothe slower vaporization there.) By the coolness. and in other ways, ifdesired, I provide in the cool region an occluding shut-oil, formed (inan alkali metal lamp) of sodium, potassium, or other alkali metal.Accordingly, I prefer a recess comparatively narrow and deep, not onlyto assure coolness, but to minimize the amount of material required init, and to cause the material to stay in the recess even when molten.Sodium melts as low as 98 C., and potassium at about 62 C.; but at suchtemperatures these molten materials are quite viscous, and readilyremain in a narrow, deep recess. At such temperatures moreover, thesemetals do not readily attack glass, nor other materials which are quitesusceptible to attack at the normal sodium lamp temperatures of around220 to 250 C. Preferably, Iprovide in the device an excess of thematerial as compared with what is used in ordinary practice, to assureplenty for the shut-oil.

When the thus shut-off cool region or recess of a vapor glow dischargedevice is traversed by a part (like a lead wire) that tends to conductheat into the recess, I preferably arrange for dissipating this heat inthe main internal space of the device, or otherwise impeding andminimizing its transmission into the cool region or recess.

Various other features and advantages of the invention will appear fromthe following description of species thereof, and from the drawing.

In the drawing, Fig. 1 is a side view of a tubular lamp (suitable foroperation on alternating current) embodying my invention in one simpleform.

Fig. 2 is a similar view showing a different form of construction.

Fig. 3 is a similar view showing yet another form of construction.

Fig. 4 is a similar view of a lamp having a neck and stem constructionat one end.

Fig. 5 is a similar view of a lamp having a neck and stem constructionat one end, and a construction like that of Fig. 1 at its other end.

The device shown in Fig. 1 is adapted for use as a glow discharge lamp,and comprises a tubular glass envelope ill with electrodes II, I laxially arranged in its opposite ends, and supported by current leadwires 12, I2 sealed through the end walls l3, 13. The exhaust tip 14 onone end wall I3 is also shown. The electrodes H, l i are here shown asof the so-called cold type,

comprising tubular nickel bases externally coated with electron-emissivematerial, such as barium oxide. The current leads [2, I2 may be of anysuitable kind that will seal into glass satisfactorily, such astungsten, molybdenum, or a copper-clad wire, all of. which are subjectto oxidation in sealing them into glass. The envelope to contains acharge of the working substance, such as sodium or other alkali metal,and may also usually contain a small amount of easily ionized gas likeneon, argon, etc., whose partial pressure in the device is around 1 or 2to 7 mm., to assist in starting the sodium or other vapor discharge.This is the more desirable in lamps using a dimcultly vaporizableworking substance like sodium-es contrasted with one that is much moreeasily vaporized like mercury.

As thus far described, the device and its details of construction areillustrative, and may be widely varied, or even radically changed.Moreover, it is to be understood that in practice the device may beoperated with such usual sodium lamp accessories as an enclosing vacuumjacket (not shown), to conserve heat; a ballast (not shown), to controlthe current rise as the device heats up after starting; a compensatingresistance, reactor, or transformer (not shown), to allow the device tobe used on ordinary A. C. lighting circuits of 110-120 volts or thelike; etc., etc. It is also to be remarked that the oxide layer on thecurrent lead I2 in the seal at each tube end I3 is liable to rapidattack by alkali metal vapor, which causes leakage at the seal; and thatin making the seals any protective coating on the glass wall is fusedand is often partially destroyed, which allows sodium attack at thefused areaand consequent objectionable blackening of the glass.

In this particular device, there are cool regions consisting of deep,narrow recesses opening into the main interior space of the envelope IIIat either end, and formed by hollow-projections I5, I5 of the envelopewall, such as short lengths of glass tubing sealed into the end wallsI3, I3, coaxially with the cylindrical envelope walls. When the innersurfaces of the envelope II) are protectively coated or glazed againstattack bythe working substance, this is preferably done after the tubesI5, I5 have been affixed to the ends I3, I3, rather than before, so thatonly the subsequently made exhaust seal I4 and lead-wire seals I6, I6will cause susceptible internal areas. These areas, however, are thevery depths of the tubes I5, I5 where they can best be protected. Thecurrent leads I2, I2 extend axially through the tubes I5, I5, and aresealed through their closed outer ends by seals I6, I6. Preferably, eachlead I2 is provided with heat-radiating means between its electrode IIand the tube I5, as by (helically) coiling the lead wire at I! to theextent of a couple of turns, more or less. While it is impossible tointerpose heat-insulating material in a lead I2 which must be a goodelectrical conductor, the length of wire in the coil I1 offers a more orless equivalent resistance to thermal conduction via the lead, and isthus thermo-insulative. The tubes I5, I5 may be as small as isconsistent with adequate mechanical strength, or as large as isconsistent with retaining the required amount of protective materialtherein. If the tubes are small enough, they will readily stay quitefull of liquid metal. In general, tubes of about in. internal diameteranswer very well, being small enough to bring capillarity into play tohelp hold a molten filling in them. The axial current leads I2, I2assist in holding liquid material in the tubes I5, I5, excepting insofaras heat transmitted by the leads may tend to vaporize the material.

Sodium or other alkali metal 'mayvbe distilled into the envelope Illthrough the usual exhaust tube at I4 (not shown), after exhaustion ofthe device, but before sealing off; or it may be introduced in ahermetic (glass) capsule which is afterward ruptured, or in other ways.By holding the device upright, first one end up and then the other, andexternally heating the envelope walls II) while or after the material isintroduced, a considerable amount of it can be gotten into the tubularrecesses I5, I5 at the outset, before the device is ever operated. Ifthe tubes l5, I5 are externally chilled while being thus charged, theinitial metal charges may coat them internally and there solidify,evencovering the Junetion between the leads I2, I2 and the glass before orwithout actually filling the entire cross-section of the tubes. Or thematerial may initially fill the sealed-up ends of the tubes I5, I5throughout their cross-section. In either case, the metal in the tubesI5, I5 embeds the leads l2, I2 adjacent the glass and forms an effectiveshut-off to protect the lead seals (and any susceptible adjacent areasof glass) against vapor attack when the device is first operated.Whether the tubes I5, I5 contain much, little, or no metal initially,they gradually fill up completely (about as shown at I8 in Fig. 1) asmore and more material condenses in them during operation. The heat ofthe leads I2, I2 tends to cause the metal surface around them to behollowed more than would otherwise be the case, but less than withoutthe heat-dissipating lead coils l1, l1. Solid or liquid, the material inthe tubes l5, I5 does not attack the parts; at ordinary temperatures,solid sodium and potassium are of a yielding, wax-like consistency, andso offer no danger of bursting the tubes I 5, I5 as a result of thermalexpansion or contraction when the-device is thrown out of operation andallowed to cool,or 'vice-versa.

In the device of Fig. 2, the axially tubular projections I5a, I5a andthe axial current leads l2, I2 in them are bent upward (in the positionof the device shown), at right angles to the axis of the envelope II).This makes the device shorter over-all than that ofFig. 1. The exhausttip Ila is shown on one of these tubes I5a, where it will be protectedby the shut-off materiaL-instead of exposed on the tube end l3 as inFig. l.

In the device of Fig. 3, the tubular projections I51), I52) do not openthrough the end walls I3b, I3b, but through the side walls of theenvelope I0 adjacent the ends; and the tubes I51), I51) are sharply benttoward oneanother, into parallelism with the axis of the envelope. Thusthe device is even shorter over-all than that of Fig. 2. The

current leads I2b, I2b extend radially of the envelope II) from theircoils I1, I! into the-tubes I527, I51), and are there bent at rightangles so as to extend axially in the tubes.

The device of Fig. 4 is of a more ordinary tubular lamp type,'with bothcurrent leads I2c, I2c introduced at the same end I30 of the envelopeIilc, through an ordinary tubular stem 20 with the usual seal press 2|and tipless" stem exhaust tube 22. The stem 20 is sealed as usual into areduced neck I5c on one envelope end I3c, while the other envelope end I30 is spherically rounded. The current leads I20, I20 carry theelectrodes II, II in the opposite ends of the envelope I00; and one ofthe leads extends the whole length-of the envelope in an insulativecover-tube 23 (of glass, or of refractory material like alumina), whichis sealed into the stem press 2I, and is offset to one side of theenvelope axis. This insulative cover 23 prevents electrical dischargebetween this long lead Ilc and the adjacent short lead I2c as well asshort circuiting between these leads by the metal in the neck I50. Onlythe short lead I20 has a coil I'Ic, since the length of the long leadserves to dissipat heat.

Here the neck I5e forms the cool recess for the sodium or othershut-off. The stem 20 is preferably made as small as possible (e. g., ofstandard automobile headlight size), and the neck I50 correspondinglysmall, though necessarily larger than in Fig. 1. However, the narrownessof the annular space around the stem 20 in the neck I50 helps to holdthe material in the neck to its very junction with the rest of theenvelope Inc. The whole neck I5e is initially or eventually filled withcondensed material (as shown at I80), embedding the whole stem 20 andthe portions of the leads I20, I20 within the neck I50, and protectingthe stem 20 if made of glass that does not resist alkali metal attack.This is advantageous because a stem of resistant glass would bedifilcult to make and seal properly. Operating this device upright andneck-down, there is no difficulty in maintaining a body of moltenmaterial completely filling the neck I5e.

The device of Fig. 5 is like that of Fig. 4 at its left-hand end, whereit has a neck I5d, etc., and like that of Fig. 1 at its right-hand end,where it has a tube I5e. Preferably, it is operated upright with neckI5d down. Its electrodes IId, ii are of an indirectly heated type suchas known in the art, and their internal (tungsten coil) heatingresistances 24, 24 are interconnected in series between the leads I2d,In by a (molybdenum) lead 25 extending axially of the envelope IIid.Thus the serially connected heating resistances 24, 24 are in parallelwith the glow discharge between the electrodes IId, IId during theoperation of the device.

In using the lamps of Figs. 1, 2, 4, and 5 in vacuum jackets (notshown), thermoinsulative refractory (asbestos) jacket gaskets 30 willpreferably be used around the tubular end projections I5, I50, I5e, I5d,and I5e,--as indicated in dot and dash lines,-to minimize loss of heatby conduction and convection in the air within the jacket around theglow discharge device.

These gaskets 30 may be made of a plurality of superposed sheets ofasbestos felt, to make them hug the surfaces of the parts I5, I5d, I5e,I5d, I5e and the internal surface of the vacuum jacket (not shown) moresnugly. Care should be taken to place them right against the tube endsI3, I30, IM and on or against the head formed by the merger of theprojection I5e with the corresponding spherical envelope end, in orderto assist in keeping the parts I5, I50, I5c, I5d, I5e as cool aspossible right up to the envelope ends. The lamp of Fig. 3 is also shownwith asbestos or other heat-dissipating gaskets 30b, 30b around thebends of its tubular projections I5b, I5b; although here such gasketscannot coact with the walls of a vacuum jacket to impede aircirculation, like those shown in Figs. 1, 2, 4, and 5.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. A vapor electric discharge device containing a substance that isvaporous during operation of the device, and comprising an envelopehaving a relatively cool region in which a portion of said vaporcondenses, a part of said region being subject to attack by the hotvapor of the substance, and a shut-off of said substance in said coolregion embedding said part and protecting it from the vapor.

2. A vapor electric discharge device containing a substance that isvaporous during operation of the device, and comprising an envelopehaving a relatively cool region in which a portion of said vaporcondenses, an inward extending part attached to the envelope wall insaid cool region and including heat-dissipating means substantially totheinside of the point of attachment, and a shut-off of said substancein said cool region traversed by said part between its said heatdissipating means and its said point of attachment.

3. A vapor electric discharge device containing an alkali metal that isvaporous during operation of the device, and comprising an elongatedtubular envelope with a relatively cool tubular recess opening laterallyfrom its-end, and a filling of alkali metal in said recess.

4. A vapor electric discharge device containing a substance that isvaporous during operation of the device, and comprising an envelopehaving a relatively cool, narrow, deep recess adapted to condense saidsubstance therein, and a wire extending into said recess and serving toretain the condensed substance therein.

5. A vapor electric discharge device containing a substance that isvaporous during operation of the device, and comprising an envelopehaving a relatively cool recess condensing and retaining a portion ofsaid substance therein, and a part in said recess that is subject toattack by the hot vapor of said substance and immune to attack by saidsubstance in a non-vaporous state, said condensed substance covering thenon-resistant part of said recess to protect said part from attack bysaid vapor.

6. A vapor electric discharge device containing a substance that isvaporous during operation of the device, and comprising an envelopehaving a tubular projection opening into its interior condensing andretaining a portion of said substance therein, and a current lead sealedthrough the wall of said tubular projection and extending through itsbore into the envelope, the joint between said current lead and the wallof said tubular projection being subject to attack by the hot vapor ofsaid substance and immune to attack by said substance in a non-vaporousstate.

7. A vapor electric discharge device containing a substance that isvaporous during operating of the device, and comprising an envelopehaving a relatively cool capillary recess condensing and retaining aportion of said substance therein, and a current lead sealed through theenvelope wall in said recess and extending therethrough into theinterior of the envelope, the joint between said current lead and saidenvelope wall being subject to attack by the hot vapor of said substanceand immune to attack by said substance in a nonvaporous state.

8. A vapor electric'discharge device containing a substance that isvaporous during operationof a substance that is vaporous duringoperation of the device, and comprising an envelope having a relativelycool recess condensing and retaining a portion of said substancetherein, and a part; attached to the envelope wall in the recess andextending therethrough into the interior of the envelope, and thereprovided with heat-dissipating means for minimizing heat transmissionvia said part into the recess.

10 10. A vapor electric discharge device containing aoeaeoe a substancethat is vaporous during operation of the device, and comprising anenvelope having a relatively cool recess condensing and retaining aportion of said substance therein, and a current lead sealed through theenvelope wall in said recess and extending therethrough into theinterior of the envelope, and there provided with heatdissipat-ing meansfor minimizing heat transmission along said lead into the recess.

THEODORE W. FRECH.

